Fuel cells are electrochemical cells in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. Fuel cells may be an alternative to the combustion of nonrenewable fossil fuels. Fuel cells produce by-products including carbon dioxide and water.
Previously some methanol fuel cells used a "reformer" to convert methanol to H.sub.2 gas for use by the fuel cells. Direct oxidation fuel cells do not use a reformer and may not require a fuel processing stage. Hence, direct feed fuel cells can offer weight and volume advantages over the indirect reformer fuel cells.
Some prior work in direct feed fuel cells used a strong acid electrolyte which can cause corrosion, degradation of catalyst and other problems that can compromise efficiency. Problems associated with such fuel cells have been well recognized in the art.
Jet Propulsion Laboratory "JPL" developed an improved liquid direct-feed fuel cell using a solid-state electrolyte, preferably a solid polymer cation exchange electrolyte membrane. The JPL fuel cell does not use liquid acidic and alkaline electrolyte and hence obviates many problems in the conventional liquid direct-feed fuel cells. The subject matter of this improvement is described in U.S. Pat. No. 5,599,638, U.S. Pat. No. 5,773,162, and U.S. patent application Ser. No. 08/827,319 (Patent Pending) filed Mar. 26, 1997, the disclosures of which are herewith incorporated by reference to the extent necessary for proper understanding.
Catalyst materials used in such fuel cells are often made from platinum. In order to reduce cost, the minimum amount of catalyst deposit is desirable.
A standard amount of catalyst utilization--loading level, is 4 mg/cm.sup.2 However, reducing the loading of catalyst on the anode from 4 mg/cm.sup.2 has lead to a significant performance decline of the membrane electrode assemblies ("MEA") in prior art. At low loading levels, e.g. 2 mg/cm.sup.2, performance is usually unstable and declines with use. This performance decline is probably due to delamination of the electrode catalyst from the membrane. Hence, a method to improve bonding of the catalyst to the membrane is desired.
At the cathode, the need for high loading appeared to result from coverage of some catalyst by water passing from the anode side through the membrane of the membrane electrode assembly. Water infiltration at the cathode rendered some cathode catalyst inactive because air can not reach the catalyst. Improved water repellency of the membrane is desired.
Methanol crossover includes the undesirable transport of methanol from the anode compartment to the cathode compartment. Methanol crossing the electrode barrier will reduce the efficiency of conversion. Crossover also contributes to the cathode high loading situation described in the previous paragraph.
Another factor that can contribute to high loading at the anode is the migration of catalyst from the anode surface into the catalyst support. This occurs when the electrode and membrane are hot-pressed together to form a membrane electrode assembly "MEA". This catalyst migration may produce negative effects: 1) Catalyst utilization efficiency declines; and 2) The porosity of the catalyst layer increases which can increase methanol crossover. Overall, catalyst migration at the anode can decrease efficiency of the catalyst and result in a general loss in MEA performance. A catalyst solution "ink" that can tolerate high temperatures while keeping the catalyst bound on the anode surface is desired to reduce catalyst migration.